vagrant: fixes for freebsd 12.1

Vagrantfile

@@ -46,11 +46,9 @@ def packages_freebsd
     pkg install -y liblz4 zstd fusefs-libs pkgconf
     pkg install -y git bash  # fakeroot causes lots of troubles on freebsd
     # for building python:
-    pkg install -y sqlite3
-    pkg install -y py27-virtualenv  # provides "virtualenv" command
-    pkg install -y python36 py36-virtualenv py36-pip
+    pkg install -y python37 py37-sqlite3 py37-virtualenv py37-pip
     # make sure there is a python3 command
-    ln -s /usr/local/bin/python3.6 /usr/local/bin/python3
+    ln -sf /usr/local/bin/python3.7 /usr/local/bin/python3
     # make bash default / work:
     chsh -s bash vagrant
     mount -t fdescfs fdesc /dev/fd